Patent GB-925750-A (GB)
Title: Hydraulically-actuated grab control system
IPC: F15B11/08
Filed: 1961-09-28
Abstract: 925,750. Hydraulic control systems. NORDDEUTSCHE MASCHINEN-UND SCHRAUBENWERKE A.G. Sept. 28, 1961 [Oct. 26, 1960], No. 34901/61. Class 69 (2). A control system for an hydraulically-actuated grab comprises a control valve 4 for connecting a pump to either a first or second conduit O, S leading to one or more units 9 for causing movement of the jaws of the grab in an opening or closing direction, respectively, and a non-return valve 5 in the second conduit arranged when the control valve is positioned for causing closing of the jaws to permit free flow of fluid to the unit or units and to prevent flow in the reverse direction. The control valve 4 and non-return valve 5 are disposed in a housing 2 having a bore 12 connected to a pump and a bore R for the return of liquid from the unit 9. A magnetically-operated pilot valve 8 for the control valve 4 is secured to the side of the housing and a valve 7 is disposed between the non-return valve 5 and second conduit S and arranged to permit free flow of liquid to the unit when the control valve is positioned to effect closing of the jaws and a restricted flow in the reverse direction. In operation, when the jaws are to be closed, the solenoid winding 62 of the pilot valve 8 is de-energized to permit a spring 68 to move the spool 64 of the valve to a position wherein a bore 20 leading from the bore 12 from the pump is disconnected from a bore 71 leading to one end of the spool 10 of the control valve 4 so that a spring 14 moves the spool to its right-hand position, as shown, wherein a bore 13 from a lower chamber 49 of the unit 9 is connected to the return bore R. The liquid from the pump passes around a groove 15 in valve 4 to a passage 27 so as to act on the end of the non-return valve 5 which is thus opened to permit the liquid to lift a ball 52 of the throttle valve 7 and pass unrestricted to the upper chamber 48 of the unit and move a piston 46 thereof downwardly to close the jaws of the grab. When the piston has moved to the end of its stroke, excess pressure in the bore 12 acts to open a relief valve 3 and by-pass liquid to the return bore R. The non-return valve 5 closes when the piston reaches the end of its stroke and prevents liquid passing from the chamber 48 when the pump is stopped. When it is desired to open the jaws, the solenoid 62 is energized to move the spool 64 of the pilot valve 8 against the spring 68 to connect the bore 70 to the bore 71 leading to the end of the spool 10 which is thus moved against the spring 14 to disconnect bore 13 from the return bore R and connect the bore 12 from the pump to bore 13 so that the pressure liquid acts in both chambers and the piston moves as a result of the differential pressure. In order to permit liquid to flow from the chamber 48, the non-return valve 5 is opened by the pressure in bore 13 acting in a chamber 38 to move a valveactuating piston 32 which abuts a rod 36, the movement of which first opens a pilot valve 31 in the non-return valve to permit liquid in conduit S to pass through holes 32a and a groove in the stem of the pilot valve and equalize the pressures on opposite sides of the non-return valve. Further movement of the rod displaces the cone 30 of the valve to let the liquid in chamber 48 pass through bore 12 and join the liquid from the pump passing through bore 13 to the chamber 49. When liquid is flowing from chamber 48, the ball 52 of throttle valve 7 is urged on to its seating and the liquid flows through throttling passages 55, 57, 56, the extent of the throttling being variable by axial adjustment of a sleeve 58. The drop in pressure across the throttle valve ensures that the pressure in chamber 38 is sufficient to open the non-return valve.